In many industrial processes, wastewater is created having high concentrations of heavy metal ions and other contaminant materials such as various anions and cations including fluorides, cyanides and hexavalent chrome. Because of the high concentration of heavy metals and other contaminant materials, the water cannot be recycled in many industrial procedures and moreover cannot be discharged to environmental outlets because of the pollutant effect of such heavy metal ions and/or other contaminant materials. In the metal finishing industry, the Environmental Protection Agency has set certain tentative discharge limits for maximum amounts of heavy metal ions which can remain in water discharged to the environment. The industry has attempted to meet the pollutant problem by several long known and other recently developed methods. In one often used method, wastewater containing heavy metal ions and other contaminant materials resulting from metal finishing rinses, is treated with an alkaline or acid material to adjust the pH and form insoluble hydroxides or other precipitates of the metals. The insoluble hydroxides or other precipitates are then separated from the wastewater. A problem here is that many of the heavy metal ions and other contaminant materials are soluble to some extent even in their hydroxide or precipitated form, thus wastewater so treated often still carries undesirably high levels of certain metal ions. In a more recent development, ion exchange methods have been employed to remove heavy metal ions and other contaminant materials. However, such methods are often expensive and complex. Other problems arise with the use of reverse osmosis techniques. High concentrations and high pressures are part of reverse osmosis operational problems. Reverse osmosis is limited to approximately 2000 parts per million (ppm) concentration and efficiency of the process is inversely proportional to the concentration.
It was believed in the art that, heavy metal hydroxides tend to form a gelatinous precipitate and thus block filter membranes by penetration into filter pores or by building a continuous gelatinous precipitate on top of a membrane face area. Thus the art often removes and avoids use of heavy metal hydroxides in filtering procedures in order to avoid the known clogging problems.